Method and apparatus for making finned tubing



Oct. 10, 1967 c 1 ETAL 3,345,726

METHOD AND APPARATUS FOR MAKING FINNED TUBING Filed Dec. 17, 1963 4 Sheets-Sheet l INVENTORE,

5%4/ 295 Zf f/zahfla z. Q B6 271? A, d'aZd'smzZ/E 10, 1967 v c. E. HICKMAN ETAL 3,345,726

METHOD AND APPARATUS FOR MAKING FINNED TUBING 4 Sheets-Sheet 2 Filed Dec. 17, 1965 1967 c. E. HlCKMAN ETAL METHOD AND APPARATUS FOR MAKING FINNED TUBING 4 Sheets-Sheet 5 Filed Dec.

3. 5 2 w mmm R w? n z. w 6A d ZB a Oct. 10, 1967 E. HlCKMAN ETAL 3,345,726

METHOD AND APPARATUS FOR MAKING FINNED TUBING Filed Dec. 1963 4 Sheets-Sheet 4 I 074m K923322595,

United States Patent 3,345,726 METHOD AND APPARATUS FOR MAKING FINNED TUBING Charles E. Hickman, Adrian, Mich., Ann Arbor Trust Company, Ann Arbor, Mich, and Kathryn Goldsmith, coexecutors of Charles E. Hickman, deceased; and Allen L. Goldsmith, Adrian, Mich., assignors to Brazeway, Inc., Adrian, Mich., a corporation of Michigan Filed Dec. 17, 1963, Ser. No. 331,231 8 Claims. (Cl. 29157.3)

This invention relates to heat exchangers of the finned tube type and to an improved method of and apparatus for assembling the fins to the tubing so as to obtain uniformly good heat transfer joints between the fins and the tubing.

Finned tube heat exchangers in which the fins are mechanically secured to the tubing without soldering or metallurgical bonding are well known in the refrigeration and air conditioning art. However, the effectiveness and uniformity of quality of the heat transfer joints between the fins and tubing leave considerable to be desired for a number of reasons. The inherent limitations of known techniques of making such heat exchangers are a contributing factor in this respect. The present invention overcomes many of the deficiencies of conventional methods and makes it possible and economically feasible to etficiently achieve uniformly good mechanical heat transfer joints between the fins and tubing in heat exchangers of this type.

A principal object of the invention isto provide for refrigeration and air conditioning uses an improved finned tube type of heat exchanger with mechanical, uniformly good heat transfer joints between the fins and the tubing.

Another object of the invention is to provide a simple and efiicient method of making finned tube heat exchangers with mechanical, uniformly good heat transfer joints between the fins and the tubing.

Another object of the invention is to provide an efficient method of making multiple bank finned tube heat exchangers from a single length of tubing.

Another object of the invention is to provide a simple, durable, andefficient apparatus for practicing such meth od.

Other and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are four sheets, which by Way of illustration show preferred embodiments of the invention and what we now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings: v

FIGURE 1 is a perspective view illustrating somewhat schematically the tube holding carrier and flattening die useful in practicing the method and showing a serpentine 'coil of tubing on the carrier in position for insertion into the flattening die;

FIGURE 2 is a cross sectional view through the flattening die in its open position with the tubing positioned therein;

FIGURE 3 is a view similar to FIGURE 2 and showing the flattening d-ie closed;

FIGURE 4 is a perspective view illustrating somewhat schematically the tube holding carrier and a bank of fins to be assembled with the flattened tubing carried by the carrier, and above the bank of fins the tool which cooperates with the mandrels for securing the tubing to the fins;

FIGURE 5 is an enlarged fragmentary sectional view of two of the mandrels taken along the line 5--5 of FIGURE 4;

FIGURE 6 is an enlarged fragmentary sectional view of the tube holding carrier illustrated in FIGURE 4;

FIGURE 7 is a sectional view through a bank of fins assembled in a nest as in FIGURE 4, with the tubing assembled with the fins and illustrating the means whereby the tubing is re-formed to secure the fins thereon;

FIGURE 8 is a view similar to FIGURE 7 after the step of re-forming the tubing to secure the fins thereon; FIGURE 9 is a perspective view of a finned tube heat exchanger made in accordance with this invention;

FIGURE 10 is an elevational view of the heat exchanger showing the end opposite to that illustrated in FIGURE 9; 7 FIGURE 11 is a sectional view taken along the line 1111 of FIGURE 10; and

FIGURE 12 is a fragmentary side elevational view of a heat exchanger made in accordance with our invention and wherein the fins have been metallurgically bonded to the tubing.

The method of our invention as illustrated includes the steps of forming a single length of round tubing 20 into a series of parallel runs 22, 24, 26, 28, 30 et al. connected by return bends 40, 42, 44, 46, 48 50 and 52; punching a series of elongated slots or holes 60, 61, 63 and 65 in a series of fins and arranging such fins in a nest or bank as illustrated in FIGURE 4 with corresponding slots aligned; partially flattening the tubing runs and the return bends at one end thereof to make the tubing oval in cross section so that it will pass through the slots; inserting the formed tubing through the slots in the bank of fins by pushing the flattened return bends of the. tubing through the slots; and re-forming the tubing runs to thereby make good metal-to-metal contact between the tubing and the edges of the fins which form the end portions of the slots, and interlock said fins and tubing.

In practicing our invention, we prefer to use small diameter thin-walled extruded round aluminum tubing made in accordance with that method covered by our prior US. Patent No. 2,964,178, issued Dec. 13, 1960. However, our technique is not limited to the use of extruded aluminum tubing, and other tubing of the kind commonly used in refrigeration and air conditioning heat exchangers, such as copper tubing and steel tubing, as well as double tubing, may be employed. We prefer to make the fins out .of aluminum fin stock when using aluminum tubing.

The tubing 20 is first bent in any suitable conventional Way into serpentine form to provide a series of parallel runs as illustrated in FIGURES 1 and 4. The was may be disposed in one or more planes so as to provide a plurality of banks of runs all formed from a single length of tubing with integral return bends and no joints and preferably with both ends of the tubing projecting from one end of the formed tubing. After the tubing is formed, it is arranged as illustrated in 'FIGURE 1 on tube holding mandrels 62. The mandrels 62 are mounted on and project from a carrier 64 with each of the mandrels 62 comprising two parts 66 and 68 which are supported by the carrier 64 so as to provide a slight gap or clearance 70 therebetween. FIGURE 2, which shows a cross section through the mandrels of FIGURE I inserted in the flattening die illustrates how the tubing runs are supported by the mandrels 62. The carrier 64 is slidably mounted for movement toward and away from the flattening die 72 between the plates of which the mandrels are inserted so as to position the tubing runs and the return bends at one end thereof between the die blocks 74, 76, and 78 of the flattening dies. Springs 80 normally separate the dies 74, 76 and 78 so that the tubing runs and return bends at one end thereof may be freely inserted and removed when the die is open, as illustrated in FIGURE 2. The flattening die includes a number of side guides 82, 84, 86, 88, 90 and 92 between which the tubing runs are inserted. After the tubing has been inserted between the die blocks of the flattening die as illustrated in FIGURE 2, the flattening die is closed under pressure as illustrated in FIGURE 3 so as to partially flatten the tubing runs and the return bends at one end thereof.

A suitable force is applied to the flattening die so as to close the die blocks as shown in FIGURE 3 and make the tubing oval in cross section. This operation also serves to straighten the tubing runs. During the flattening operation the parts 66 and 68 of the mandrels are brought together as shown in FIGURE 3, and the mandrels 62 cooperate with the guides 82, 84, 86 et al. to accurately form the tubing to predetermined oval cross section. The parts 66 and 68 of the mandrels 62 are initially held apart by any suitable means on the carrier 64 to provide a gap between the parts 66 and 68. This gap is closed by the ovalizing of the tubing during the flattening operation. The mandrel parts 66 and 68 are held together by a series of bolts 91 with a coil spring 93 confined between the head of the bolt and the part 66 and a coil spring 94 confined between the nut on the bolt and the part 68. After the flattening operation, the tube carrier and mandrels of FIGURE 1 are withdrawn from the flattening die and the tubing is then ready for insertion into the slots of a bank'of fins as shown in FIGURE 4. Where oval tubing of the desired size is available, the'flattening step may be omitted, although it is preferable to start with round tubing, bend it, and then ovalize it as the flattening die accurately shapes and straightens the tubing preparatory to its insertion in the slots in the bank of fins.

The bank of fins comprises a series of planar blanks preferably cut from strip fin stock and punched to provide a series of dumbbell-shaped slots to receive the formed andflattened tubing. The fins 103 are arranged in a nest or comb, as illustrated in FIGURE 4, with the slots accurately aligned and disposed between angular end plates 100, 102 which are also similarly slotted. The fins and end plates are disposed in parallel to each other and spaced, for example, five to the inch. The elongated slots each-comprise two enlarged round end portions 104 and 106 connected by a narrow slot 108. The diameter of the round portions 104, 106 is preferably very slightly less than the nominal diameter of the tubing after it is reformed, while the width of the narrow interconnecting portion 108 of each of the slots is preferably slightly greater than the minor diameter of the flattened tubing. The runs of tubing and the return bends are carried by the fixture 64 so as to accurately line up with the dumbbellshaped slots in the bank of fins as illustrated in FIGURE 4, and thereafter the flattened tubing and the bank of fins are brought together and telescoped so as to insert the tubing into the slots. Since the minor diameter of the tubing is no greater than the thickness of the narrow portions 108 of'the dumbbell-shaped slots, the fins can be readily positioned on the tubing with practically no drag or interference between the tubing and the edges of the slots, the mandrels 62 serving to accurately hold and support the tubing during insertion.

After the bank of fins has been assembled on the tubing as just described, the mandrels 62 are expanded as illustrated in FIGURE 8 so as to re-form the tubing to a round or enlarged cross section greater than the width of the narrow intermediate portion of the slot. For this purpose, a series of wedges carried by a plate 122 are forced downwardly from the position illustrated in FIG- URE 7 to that shown in FIGURE 8 so as to expand the mandrels 62. Each mandrel is provided with a series of notches 124 which form cams 126 which are engaged by the wedges 120 as they move downwardly so as to separate the parts 66 and 68 of the mandrels 62. This causes the parts 66 and 68 to react on the oval tubing throughout the length of the runs while the latter is positioned against the ends of the slots so as to re-form such tubing to its round cross section, thus causing the tubing in the round portions 106 and 104 of the slots to conform to such round portions. This brings the tubing into intimate and firm engagement with the edges of the fins which form the round portions 106 and 104 of the slots so as to provide good metal-to-metal contact between the tubing and each of the fins. This also serves to lock and secure the tubing in the enlarged ends of the slots and firmly anchors the fins and end plates on the tubing without soldering, brazing, or metallurgical bonding operations. Thereafter the plate 122 is elevated so as to disengage the wedges 120 from the mandrels 62. This frees the mandrel from the tubing runs and permits the latter to be freely withdrawn from the slots in the fins. The fins and tubing are thus completely assembled and may be freely re moved from the nest or comb.

While the method just described makes it possible to assemble a finned tube heat exchanger without soldering or otherwise metallurgically bonding the fins to the tubing, it may in some cases be desirable to so unite the fins and tubes. This may be done in any of a variety of conventional ways. For example, if the tubing and fins are of aluminum, the fins may be precoated with a suitable brazing or soldering flux so that after the mechanical assembly of the fins and tubing has been completed, the assembly may be put through a brazing oven or, alternatively if the tubing is steel tubing and the fins are steel, the fins may be pro-solder coated and then put through a baking oven to melt the solder and form solder joints between each of the fins and each run of tubing as shown in FIGURE 12.

Using our invention it is possible to make a multiple bank heat exchanger with more than two rows of serpentine tubing from a single length of tubing with no joints. Our method makes for easy insertion of the tubing in the fin slots while providing uniformly good metal-to-metal contact between the tubing and the fins. Since the slots in the fins are closed, the fin stock is in tension during the re-forming of the tubing, making it possible to use thinner gauge fin stock than may otherwise be used, and also making the location and orientation of the slots substantially less critical. With our method the outer edges of the fins are continuous and less subject to damage than the so-called side entry type of heat exchangers. With our invention the end plates of the heat exchanger may be assembled to the tubing at the same time as the fins and thus no extra operation is required for this purpose, as is usually the case.

A wide range of tubing and fin sizes may be used in practicing the invention. As a specific example for a refrigeration heat exchanger, the aluminum tubing may be of a size within the range of five-sixteenths to threeeighths of an inch, with the tubing runs spaced on one inch centers.

The elongated slots in the fins and end plates are preferably shaped so as to provide enlarged end portions in which the tubing is locked and more than of contact between the tubing and each fin. Preferably the elongated slots in the fins are made without flanges or collars so that under the metal deforming pressure applied to the tubing to reshape it the cut metal edges of the fin slots bite into the tube metal to achieve intimate metal-to-meal contact with the tubing metal during the re-forming operation to provide a good mechanical heat transfer joint between the tubing and the fins. Thus our method compensates for the variations in dimensions encountered in the slots and tubing due to normal manufacturing tolerances and assures a tight mechanical joint between the tubing and each of the fins.

While we have illustrated and described preferred embodiments of our invention, it is understood that these are capable of modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims.

We claim:

1. That method of assembling a finned tube heat exchanger which includes the steps of forming a plurality of fins each with a like series of elongated slots having enlarged ends, positioning said fins in a bank with corresponding slots in alignment, forming a single length of tubing into serpentine form so as to provide a series of parallel runs with adjacent runs forming a pair and connected by a return bend, flattening said runs and the return bends at one end thereof so that the major cross sectional diameter of the flattened tubing of the runs of each pair lies in the same plane as that of the return bend interconnecting such runs and so that the cross sectional diameter transverse thereof will pass through the interthereby to lock said tubing runs in the enlarged portions of said slots and secure said fins in spaced relation on said tubing runs.

4. That method according to claim 3 including the step of straightening said tubing runs during the step of flattening said runs.

5..That method of assembling a finned tube heat exchanger which includes the steps of forming a bank of fins, each with a like series of elongated slots having enlarged ends, with corresponding slots in alignment, forming a single length of tubing into a series of parallel runs with adjacent runs forming a pair connected by a return bend and with the tubing of such runs and the return bends at one end oval in cross section so that they will pass through such slots, telescoping the formed tubing and bank of fins together so as to pass the return bends at mediate portion of said slots, telescoping the serpentine tubing and bank of fins so as to pass the flattened return bends at one end of the formed tubing through the intermediate portions of the slots in the fins and to position the flattened tubing runs in the enlarged portions at the ends of such slots, and simultaneously applying to the opposing surfaces of the runs of each said pair of runs metal deforming forces directed toward the enlarged portions of the slot in which such runs are located whereby the fins are placed in tension and utilized as an anvil against which said forces are applied through the tubing runs to force said runs into intimate metal-to-metal engagement with the edges of the fins defining the enlarged portions of said slots thereby to secure said fins'in spaced relation on said tubing runs and lock said tubing runs in the enlarged portions of said slots.

2. That method according to claim 1 including the step of straightening said tubing runs during the step of flattening said runs.

3. That method of assembling a finned tube heat exchanger which includes the steps of forming a plurality of fins each with a like series of elongated slots disposed in at least two side by side rows, the ends of said slots being enlarged, positioning said fins in a bank with corresponding slots in alignment, forming a single length of round tubing into serpentine form so as to provide a series of parallel runs disposed in at least two side by side rows with adjacent runs forming a pair and connected by a return bend, flattening said runs and the return bends at one end thereof so that the major cross sectional diameter of the flattened tubing of the runs of each pair lies in the same plane as that of the return bend interconecting such runs and so that the cross sectional diameter transverse thereof will pass through the intermediate portion of said slots, telescoping the serpentine tubing and bank of fins so as to pass the flattened return bends at one end of the formed tubing through the intermediate portions of the slots in the fins and to position the flattened tubing runs in the enlarged portions at the ends of sue-h slots, and simultaneously applying to the opposing surfaces of the runs of each said pair of runs oppositely directed metal deforming forces whereby the fins are placed in tension and utilized as an anvil against which said forces are applied through the tubing runs to force said runs into intimate metal-to-metal engagement with the edges of the fins defining the enlarged portions of said slots and restore said runs to a round condition one end thereof through the intermediate portions of the slots in the fins and to position the tubing runs in the enlarged portions of such slots, and simultaneously applying to the opposing surfaces of the runs of each said pair of runs metal deforming forces directed toward the enlarged portions of the slot in which such runs are located whereby the fins are placed in tension and utilized as an anvil against which said forces are applied through the tubing runs to force said runs into intimate metal-t0- metal engagement with the edges of the fins defining rue enlarged portions of said slots thereby to secure said fins in spaced relation on said tubing runs and lock said tubing runs in the enlarged portions of said slots.

6. Apparatus for assembling a finned tube heat exchanger comprising a fixture for supporting a bank of slotted fins, a tube carrier including a plurality of expansible mandrels each adapted to be disposed between and to support adjacent runs of a serpentine coil of tubing, said mandrels and the tubing supported thereby being insertable through the slots in said bank of fins while the latter is supported on said fixture, and means for expanding said mandrels in the plane of said tubing runs While the tubing is inserted in said slotted fins so as to force said tubing runs against the ends of the slots in the fins and thereby reshape the cross section of the tubing runs and interlock said fins and tubing.

7. Apparatus for assembling a finned tube heat exchanger comprising a fixture for supporting a bank of slotted fins, a tube carrier including a plurality of mandrels each adapted to be disposed between adjacent runs of a serpentine coil of tubing and insertable with the tubing supported thereon through the slots in said bank of fins While the latter is supported on said fixture, said mandrels each having relatively movable portions, and means for moving said portions of said mandrels relatively to each other in opposite directions outwardly against the tubing runs while the tubing is inserted in said fins so as to apply metal deforming pressure to the tubing runs thereby to reshape the cross section of the tubing runs and force said runs into intimate metal-to-metal engagement with the edges of the fins defining the ends of the slots in the fins.

8. Apparatus for assembling a finned tube heat exchanger of the type comprising a serpentine coil of tubing having a series of slotted fins thereon with adjacent parallel runs of the tubing extending through an elongated slot in each fin, comprising a fixture for supporting a bank of slotted fins, a tube carrier for holding the coil of tubing and telescoping the runs of the tubing through the slots in the bank of fins while the latter is supported on said fixture, and movable means engageable with the opposing surfaces of adjacent runs of the tubing while the tubing is inserted in the slots in said fins and adapted to apply metal deforming pressure against said runs in opposite directions to reshape the cross sections of the tubing runs and force said runs into intimate metal-tometal engagement with the edges of the fins defining the ends of the slots.

References Cited UNITED STATES PATENTS Przyborowski 29-202 Kramer 165-151 XR Kritzer 165-482 XR Kramer 29157.3 Greer 29157.3 X Wright 165-181 X Thomas et a1. 29-157.3

8 10/1963 Sirnpelaar 165--181 12/1963 Kritzer 29202 6/1964 Huggins et a1. 29-157.3 6/1965 Farris 165-181 FOREIGN PATENTS 5/1957 Germany. 8/1961 Great Britain.

CHARLIE T. MOON, Primary Examiner.

Examiners.

H. D. HOBART, N. R. WILSON, Assistant Examiners. 

1. THAT METHOD OF ASSEMBLING A FINNED TUBE HEAT EXCHANGER WHICH INCLUDES THE STEPS OF FORMING A PLURALITY OF FINS EACH WITH A LIKE SERIES OF ELONGATED SLOTS HAVING ENLARGED ENDS, POSITIONING SAID FINS IN A BANK WITH CORRESPONDING SLOTS IN ALIGNMENT, FORMING A SINGLE LENGTH OF TUBING INTO SERPENTINE FORM SO AS TO PROVIDE A SERIES OF PARALLEL RUNS WITH ADJACENT RUNS FORMING A PAIR AND CONNECTED BY A RETURN BEND, FLATTENING SAID RUNS AND THE RETURN BENDS AT ONE END THEREOF SO THAT THE MAJOR CROSS SECTIONAL DIAMETER OF THE FLATTENED TUBING OF THE RUNS OF EACH PAIR LIES IN THE SAME PLANE AS THAT OF THE RETURN BEND INTERCONNECTING SUCH RUNS AND SO THAT THE CROSS SECTIONAL DIAMETER TRANSVERSE THEREOF WILL PASS THROUGH THE INTERMEDIATE PORTION OF SAID SLOTS, TELESCOPING TGHE SERPENTINE TUBING AND BANK OF FINS SO AS TO PASS THE FLATTENED RETURN BENDS AT ONE END OF THE FORMED TUBING THROUGH THE INTERMEDIATE PORTIONS OF THE SLOTS IN THE FINS AND TO POSITION THE FLATTENED TUBING RUNS IN THE ENLARGED PORTIONS AT THE ENDS OF SUCH SLOTS, AND SIMULTANEOUSLY APPLYING TO THE OPPOSING SURFACES OF THE RUNS OF EACH SAID PAIR OF RUNS METAL DEFORMING FORCES DIRECTED TOWARD THE ENLARGED PORTIONS OF THE SLOT IN WHICH SUCH RUNS ARE LOCATED WHEREBY THE FINS ARE PLACED IN TENSION AND UTILIZED AS AN ANVIL AGAINST WHICH SAID FORCES ARE APPLIED THROUGH THE TUBING RUNS TO FORCE SAID RUNS INTO INTIMATE METAL-TO-METAL ENGAGEMENT WITH THE EDGES OF THE FINS DEFINING THE ENLARGED PORTIONS OF SAID SLOTS THEREBY TO SECURE SAID FINS IN SPACED RELATION ON SAID TUBING RUNS AND LOCK SAID TUBING RUNS IN THE ENLARGED PORTIONS OF SAID SLOTS.
 6. APPARATUS FOR ASSEMBLING A FINNED TUBE HEAT EXCHANGER COMPRISING A FIXTURE FOR SUPPORTING A BANK OF SLOTTED FINS, A TUBE CARRIER INCLUDING A PLURLITY OF EXPANSIBLE MANDRELS EACH ADAPTED TO BE DISPOSED BETWEEN AND TO SUPPORT ADJACENT RUNS OF A SERPENTINE COIL OF TUBING, SAID MANDRELS AND THE TUBING SUPPORTED THEREBY BEING INSERTABLE THROUGH THE SLOTS IN SAID BANK OF FINS WHILE THE FATTER IS SUPPORTED ON SAID FIXTURE, AND MEANS FOR EXPANDING SAID MANDRELS IN THE PLANE OF SAID TUBING RUNS WHILE THE TUBING IS INSERTED IN SAID SLOTTED FINS SO AS TO FORCE SAID TUBING RUNS AGAINST THE ENDS OF THE SLOTS IN THE FINS AND THEREBY RESHAPE THE CROSS SECTION OF THE TUBING RUNS AND INTERLOCK SAID FINS AND TUBING. 